The main parts of our structure.

structures.py

class Document:
    def __init__(self, document_text):
        self.raw = document_text
        self.sentences = sentencize(self.raw)
        self._index = 0

#[...]

class Sentence:
    def __init__(self, start_position, end_position, raw_document_reference):
        self.start_pos = int(start_position)
        self.end_pos = int(end_position)
        self._document_string = raw_document_reference
        self.next_sentence = None
        self.previous_sentence = None
        self.tokens = tokenize(self._document_string[self.start_pos:self.end_pos])
        self._index = 0

#[...]

class Token:
    def __init__(self, start_position, end_position, raw_sentence_reference, SOS = False, EOS = False):
        self.start_pos = int(start_position)
        self.end_pos = int(end_position)
        self._sentence_string = raw_sentence_reference
        self.next_token = None
        self.previous_token = None
        self.SOS = SOS
        self.EOS = EOS